1. Field of the Invention
The present invention relates to a hollow fiber membrane oxygenator for removing carbon dioxide from blood and oxygenating the blood in an extracorporeal blood circulation and, more particularly, to the hollow fiber membrane oxygenator of external blood circulation type.
2. Description of Related Art
A generally employed hollow fiber membrane oxygenator using porous membrane has been widely applied to a device for extracorporeal blood circulation, a device for assisting cardiopulmonary blood circulation and the like used in cardiotomy operated for cardiopathy. The membrane type oxygenator is composed mainly of hollow fiber membranes through which gas is transferred, i.e., oxygen is admitted into blood and carbon dioxide is removed from blood.
Two methods of blood circulation to the membrane type oxygenator can be used, one is an internal perfusion method and the other is an external perfusion method. The former method allows blood to flow to the inner side of the hollow fiber membranes and gas to flow to the outer side thereof. The latter method allows blood to flow to the outer side of the hollow fiber membranes and gas to flow to the inner side thereof.
The membrane type oxygenator of external perfusion type has become more popular than that of internal perfusion type because of higher mass transfer capability and lower degree of pressure loss. The aforementioned membrane type oxygenator of external perfusion type, however, tends to cause turbulence in the blood flow, which is likely to adversely affect adhesion and activation characteristics of blood platelet. In view of the above-described aspect, the oxygenator of internal perfusion type may be considered to be superior to the external perfusion type.
Japanese Patent Application Laid-Open No. 62-172961 discloses a membrane type oxygenator coated with benzylalkylammonium-heparin composite. This oxygenator, however, causes exfoliation of the composite into blood during its operation.
The above-described oxygenator may be coated with hydrophilic polymer. In such a case, when using porous membranes for gas transfer, the blood plasma component will penetrate into micropores and leak through the membrane, thus degrading gas transfer capability.
Japanese Patent Application Laid-Open No. 4-152952 discloses bio-compatible material formed of alkoxyalkyl(meta)acrylate, which can be applied to the membrane of the membrane type oxygenator. However it is practically difficult to form the hollow fiber membrane for the membrane type oxygenator directly from the alcoxyalkyl(meta)acrylate. If the hollow fiber membrane for the membrane type oxygenator is coated with alkoxyalkyl(meta)acrylate using methanol solution thereof, it flows into micropores of the hollow fiber membrane. As a result, the blood plasma component will penetrate into micropores during operation of the oxygenator and leak through the membrane, thus degrading the gas transfer capability.
In view of foregoing, it is an object of the present invention to provide a hollow fiber membrane oxygenator of external blood circulation type which minimizes adhesion and activation of the blood platelet and prevents leakage of blood plasma component.
In order to achieve the object, there is provided a hollow fiber membrane oxygenator comprising a housing and a lot of porous hollow fiber having a large number of porous hollow fiber membranes for gas transfer housed in the housing, allowing blood to flow through outer surface of the hollow fiber membrane and oxygen-containing gas to flow through inside thereof. In the hollow fiber membrane oxygenator, an outer surface or an outer layer of the hollow fiber membrane as a blood-contacting portion is coated with synthetic polymer mainly formed of alkoxyalkyl(meta)acrylate containing a C(1-4)alkoxy group and a C(1-4)alkyl group; and an intermediate layer or an inner layer of the hollow fiber membrane has substantially no synthetic polymer existing therein.
In order to further achieve the object, there is provided a hollow fiber membrane oxygenator comprising a housing and a lot of porous hollow fiber membranes for gas transfer housed in the housing, allowing blood to flow through outer surface of the hollow fiber membrane and oxygen-containing gas to flow through inside thereof. In the hollow fiber membrane oxygenator, an outer surface or an outer layer of the hollow fiber membrane as a blood-contacting portion is coated with synthetic polymer mainly formed of alkoxyalkyl(meta)acrylate containing repetitive combination of the unit shown in the following chemical formula 1; 
(where R1 represents C(1-4)alkylene, R2 represents C(1-4)alkyl, and R3 represents H or CH3 respectively.)
and an intermediate layer or an inner layer of the hollow fiber membrane has substantially no synthetic polymer existing therein.